martinbn
Science Advisor
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To call this absolute simultaneity is very misleading. And what do you mean by clocks once synchronized? Once in what frame?
Any "frame" of the one event called entanglement. The common start of the two world line.To call this absolute simultaneity is very misleading. And what do you mean by clocks once synchronized? Once in what frame?
This is a very good example for why I thik that quantum states are better interpreted in an epistemic sense and why the collapse hypothesis leads to problems with locality and causality.vanhees71.. may I know what is your answer to the above question by name123?
I'm kinda confused about your position.. do you believe that in entanglement experiments like Clauser and Aspect experiments.. it's due to common causes like red and blue socks being determined from the origin? But in the experiments that violate Bell's Inequality, there were correlations. Or maybe you believed there were correlations but it was not "non-local" because there is no reality.. hence there is nothing to be local about (so spooky at distance is false)? (if so, then this is reasonable). Or do you indeed believe Bell's Inequality is violated due to some loophole that still proves it's like red and blue socks from the initial preparation (this was actually believed by Einstein (the EPR arguments) but disproven by Bell's Experiments that showed there were really correlations even if the entangled particles were light years apart).
Yes. Thanks for the details. Good to know at least you still believe in Bell's Theorem. I thought you were arguing in terms of Einstein EPR days where Einstein believed there was no correlations and there were hidden variables (akin to the red and blue socks being determined from beginning).This is a very good example for why I thik that quantum states are better interpreted in an epistemic sense and why the collapse hypothesis leads to problems with locality and causality.
My view is that the correlations, as all probabilistic relations of quantum systems, are described by the state of the system, and the state of the system is determined by preparation. The preparation in that case is when the entangled photon pair is created (e.g., by parametric downconversion by shooting a laser beam into a crystal). When A measures her photon's polarization state (her photon is defined by that it is registered by the detector at A's place), she immediately also knows the polarization state of B's photon (his photon is defined by that it is registered by the detector at B's place, which can be very far distant from A's detector). For B nothing has changed. He simply expects an unpolarized photon and gets with 50% probability the one or the other polarization when he measures it.
Let's now assume that A's detector is very close to the photon source, and B's very far, such that A measures her photon earlier than B. In other words, the measurement processes are assumed to happen as time-like separated events. Then "collapse" happens definitely at different times for A than for B: A changes the state of the photon pair due to her measurement result much earlier than B. Still, there is no contradiction by what's known to A and B concerning the outcome of their mesaurements. Both A's and B's photons are exactly unpolarized, i.e., the polarization state if maximally indetermined.
There's, of course, also no problem when the measurement processes are realized at space-like distances. Then you can always find a reference frame, where A and B register their result simultaneously or another reference frame, where A registers her result before B or again another frame, where B registers his result before A. Still there's no contradiction, because both, A and B always just find that their photons sent from the source of entangled photon pairs are precisely unpolarized.
When A and B compare their measurement protocols (always keeping detailed track about the time, when they registered their measurement outcome to be sure to relate always the pairs which where created together at the source), they find in any case the 100% correlations due to the preparation of the photon pairs in the polarization-entangled state.
Of course, here I made two assumptions: (a) the polarization measurements are local events as described by standard QED and thus the linked-cluster principle is valid, i.e., A's measurement cannot instantaneously affect B's photon and/or measurement apparatus (implied by microcausality) and (b) that all there is possible to be known about photons is what is described by quantum states, and since this is probabilistic knowledge (some may think only) it refers to ensembles of equally prepared quantum systems, i.e., the probabilistic information described by the prepared state can only be tested by collecting "enough statistics", i.e., using a sufficiently large ensemble.
The problems start, whenever you try to give more meaning to the quantum state then is implied by this minimal interpretation. Some think (in the past Einstein and Schrödinger were the most prominent physicists to do so) that this is not a complete description of nature since "in reality" (whatever "reality" means to them) all possible observables should have determined values always. It's not completely ruled out that maybe somebody one day finds some satisfactory theory, where this is the case, but Bell's work and the empirical precise findings with respect to it, imply that such a deterministic hidden-variable theory must be non-local, and so far there seems not to be a satisfactory such kind of theory in the relativistic realm.
This is even less clear. What is a frame (in quotes) of one event?Any "frame" of the one event called entanglement. The common start of the two world line.
In any frame, there is only one event where entanglement start. I cannot be more clearer sorry.This is even less clear. What is a frame (in quotes) of one event?
When the clocks are spatially separated, how do you know they display "the same time"? Giving meaning to that statement requires a simultaneity convention, which is equivalent to choosing an inertial frame."Absolute simultaneity" is defined by clocks once synchronized displaying the same time.
What does this mean?the "simultaneity" of entanglement correlation
But then the entangled particles move apart, so they are spatially separated. See my previous post.In any frame, there is only one event where entanglement start
Know ? I "know" it because I can compute any particle 4D path (and proper time along it), and pick the event pair whee both clock display the same time.When the clocks are spatially separated, how do you know they display "the same time"?
No. The simultaneity of convention is when synchronized clock display the same time. There is no preferred frame involved here. Any frame will do.Giving meaning to that statement requires a simultaneity convention, which is equivalent to choosing an inertial frame.
It means both measure can done at a perfectly valid absolute proper time. Simultaneity didn't disappear because different frame have a different perspective on some ordering. Events only happen once at one place, that's called causality.What does this mean?
Ah, ok. But then you have to deal with the twin paradox. You can separate your clocks and then bring them back together, and they won't read the same time--they will be sitting right next to each other, but reading different times. So which one is the "right" time--the time that is "absolute"?I "know" it because I can compute any particle 4D path (and proper time along it), and pick the event pair whee both clock display the same time.
That's why I think that the only mathematical object which can be "real" in the sense that it "faithfully represents external reality" is the state vector itself.The problems start, whenever you try to give more meaning to the quantum state then is implied by this minimal interpretation. Some think (in the past Einstein and Schrödinger were the most prominent physicists to do so) that this is not a complete description of nature since "in reality" (whatever "reality" means to them) all possible observables should have determined values always. It's not completely ruled out that maybe somebody one day finds some satisfactory theory, where this is the case, but Bell's work and the empirical precise findings with respect to it, imply that such a deterministic hidden-variable theory must be non-local, and so far there seems not to be a satisfactory such kind of theory in the relativistic realm.
Your terminology is very strange. For example, if we take my world line that of my great-great grandfather, when he was born his clock showed 0, when I was born so did mine. You would say that these two events a simultaneous, then when he was 10year, and when I was 10year, are two events that are simultaneous as well.Know ? I "know" it because I can compute any particle 4D path (and proper time along it), and pick the event pair whee both clock display the same time.
No. The simultaneity of convention is when synchronized clock display the same time. There is no preferred frame involved here. Any frame will do.
It means both measure can done at a perfectly valid absolute proper time. Simultaneity didn't disappear because different frame have a different perspective on some ordering. Events only happen once at one place, that's called causality.
The problem with Everettian accounts is not weirdness. I can accept weirdness, and so can most physicists. The problem is that at this moment the role of probability in the interpretation is still unclear. The interpretation can be kindasorta described in words, but no one has, to my knowledge, shown a convincing derivation that observers in this interpretation should split in such a way that, if they perform experiments, Born's rule is observed. Though it's been almost 30 years, the situation is not qualitatively different from the one described here (also see a small, more recent update here).In that sense Everett's approach, upgraded by decoherence, is a rather logical consequence of a simple philosophical position plus standard quantum mechanics. The only problem is to accept the weird consequences.
I agree in principle that there are open issues.The problem is that at this moment the role of probability in the [Everett] interpretation is still unclear ... no one has, to my knowledge, shown a convincing derivation that observers in this interpretation should split in such a way that, if they perform experiments, Born's rule is observed.
It doesn't b/c it seems that you are looking for explanations. :-)As scientists we need to keep philosophical interpretations of unexplained phenomena to a minimum. Keep an open mind, question everything & sooner or later, usually much later, the answers will come. ... I suppose it puts me in the "shut up and calculate" club.
Thanks for mentioning Kent.with Everettian accounts is not weirdness. I can accept weirdness, and so can most physicists. The problem is that at this moment the role of probability in the interpretation is still unclear. The interpretation can be kindasorta described in words, but no one has, to my knowledge, shown a convincing derivation that observers in this interpretation should split in such a way that, if they perform experiments, Born's rule is observed.
Though it's been almost 30 years, the situation is not qualitatively different from the one described here (also see a small, more recent update here).
I couldn't agree more with this part of your posting. Indeed QT doesn't contradict this "simple philosophical position" at all. Only the notion of what a state is. In classical physics it's described by a point in phase space, in QT by the statistical operator of the system. The main difference between the classical description and quantum description is that in the classical case by the complete knowledge of the state one knows the values of all possible observables of this system (i.e., the values of all observables are always determined), while in QT only a well-defined class of observables take determined values, when any (pure or mixed) state of the system is prepared.That's why I think that the only mathematical object which can be "real" in the sense that it "faithfully represents external reality" is the state vector itself.
The definition of "external reality" is quite simple. This morning I got up and went to the bathroom. I believe the bathroom did exist all over night as part of "external reality"; it did not "become real" by being observed or used in the morning. Newton's equations of motion, conservation of energy etc. describing or predicting the continuously existence of the bathroom, and the bathroom itself have - for me - more than a pure epistemic meaning.
When talking about the quantum world we have to accept different laws of nature, but we need not give up this simple view on "external reality". Quantum mechanics is - in contrast to what many lectures and textbooks are trying to explain - perfectly consistent with this paradigm, once we accept that the mathematical entity we have to use as a "representation of external reality" is not a collection of classical properties like position, momentum etc. but the state vector itself.
I never understood the point of Everett's interpretation, let alone even in this modern form as "many-worlds interpretation" with the world branching into many parallel universes at any observation someone does on anything he or she observes, which also brings in the famous funny question by Bell, whether the observation of something by an amoeba is enough to cause a collapse (or in the MW interpretation the branching of the world) or whether you need some "more intelligent being" like a dog, monkey or human (who knows, how intelligent an amoeba maybe might be, but we just don't know it ;-)).In that sense Everett's approach, upgraded by decoherence, is a rather logical consequence of a simple philosophical position plus standard quantum mechanics. The only problem is to accept the weird consequences.
For me, all statements that quantum mechanics must not or cannot talk about "external reality" are fundamentally flawed. This is Bohr's legacy which Everett at al. try to overcome.
This won't happens for photon, but for entangled electron, this would give an interesting setup, if half the electron are sent into an accelerator ring then slowed down for comparison (if entanglement could resit such a trip).Ah, ok. But then you have to deal with the twin paradox. You can separate your clocks and then bring them back together, and they won't read the same time--they will be sitting right next to each other, but reading different times. So which one is the "right" time--the time that is "absolute"?
That would be, if both clock would have been synchronized. Have they ?Your terminology is very strange. For example, if we take my world line that of my great-great grandfather, when he was born his clock showed 0, when I was born so did mine. You would say that these two events a simultaneous, then when he was 10year, and when I was 10year, are two events that are simultaneous as well.
Find, thanks (but I am curious to understand how you can agree to my realist or even platonist position)I couldn't agree more with this part of your posting. Indeed QT doesn't contradict this "simple philosophical position" at all. Only the notion of what a state is. In classical physics it's described by a point in phase space, in QT by the statistical operator of the system. The main difference between the classical description and quantum description is that in the classical case by the complete knowledge of the state one knows the values of all possible observables of this system (i.e., the values of all observables are always determined), while in QT only a well-defined class of observables take determined values, when any (pure or mixed) state of the system is prepared.
This is just to increase circulation. I don't give a damn.... let alone even in this modern form as "many-worlds interpretation" with the world branching into many parallel universes at any observation ...
That is an interesting question, yes.... which also brings in the famous funny question by Bell, whether the observation of something by an amoeba is enough to cause a collapse (or in the MW interpretation the branching of the world) or whether you need some "more intelligent being" like a dog, monkey or human (who knows, how intelligent an amoeba maybe might be, but we just don't know it ;-)).
This is a possible consequence, but not necessarily a logical one. It simply denies the idea to let science provide realistic (ontic) explanations. Of course yours is one possible philosophical position, but there are others. They may not be yours, but they do not go away.I think the logical consequence is the minimal interpretation, according to which QT is a formalism to describe probabilistically what we observe objectively in this real world, which you describe above. Indeed, as the name says, the quantum state describes the state of the system, and it's not a state vector but the statistical operator (or equivalently in the case of pure states, which are in general quite rare and must be carefully prepared in the lab, rays in Hilbert space).
I still do not understand your position.This is a very good example for why I thik that quantum states are better interpreted in an epistemic sense and why the collapse hypothesis leads to problems with locality and causality.
My view is that the correlations, as all probabilistic relations of quantum systems, are described by the state of the system, and the state of the system is determined by preparation. The preparation in that case is when the entangled photon pair is created (e.g., by parametric downconversion by shooting a laser beam into a crystal). When A measures her photon's polarization state (her photon is defined by that it is registered by the detector at A's place), she immediately also knows the polarization state of B's photon (his photon is defined by that it is registered by the detector at B's place, which can be very far distant from A's detector). For B nothing has changed. He simply expects an unpolarized photon and gets with 50% probability the one or the other polarization when he measures it.
Let's now assume that A's detector is very close to the photon source, and B's very far, such that A measures her photon earlier than B. In other words, the measurement processes are assumed to happen as time-like separated events. Then "collapse" happens definitely at different times for A than for B: A changes the state of the photon pair due to her measurement result much earlier than B. Still, there is no contradiction by what's known to A and B concerning the outcome of their mesaurements. Both A's and B's photons are exactly unpolarized, i.e., the polarization state if maximally indetermined.
There's, of course, also no problem when the measurement processes are realized at space-like distances. Then you can always find a reference frame, where A and B register their result simultaneously or another reference frame, where A registers her result before B or again another frame, where B registers his result before A. Still there's no contradiction, because both, A and B always just find that their photons sent from the source of entangled photon pairs are precisely unpolarized.
When A and B compare their measurement protocols (always keeping detailed track about the time, when they registered their measurement outcome to be sure to relate always the pairs which where created together at the source), they find in any case the 100% correlations due to the preparation of the photon pairs in the polarization-entangled state.
Of course, here I made two assumptions: (a) the polarization measurements are local events as described by standard QED and thus the linked-cluster principle is valid, i.e., A's measurement cannot instantaneously affect B's photon and/or measurement apparatus (implied by microcausality) and (b) that all there is possible to be known about photons is what is described by quantum states, and since this is probabilistic knowledge (some may think only) it refers to ensembles of equally prepared quantum systems, i.e., the probabilistic information described by the prepared state can only be tested by collecting "enough statistics", i.e., using a sufficiently large ensemble.
The problems start, whenever you try to give more meaning to the quantum state then is implied by this minimal interpretation. Some think (in the past Einstein and Schrödinger were the most prominent physicists to do so) that this is not a complete description of nature since "in reality" (whatever "reality" means to them) all possible observables should have determined values always. It's not completely ruled out that maybe somebody one day finds some satisfactory theory, where this is the case, but Bell's work and the empirical precise findings with respect to it, imply that such a deterministic hidden-variable theory must be non-local, and so far there seems not to be a satisfactory such kind of theory in the relativistic realm.
Let’s assume that all systems you have “prepared” are members of a pure ensemble – described by, maybe, one unique superposition state. Without assuming hidden variables, all of the systems in such a pure ensemble must be "physically" in the same state – otherwise whatever makes their states different would be a hidden variable, some "unknow preparation effect". Thus, when saying that a quantum state applies to ensembles and that the ensembles are not necessarily homogeneous, you have simply to answer the following physical question: “What differentiates the members of the ensemble from each other?” No answer means: Hiding a „hidden variable interpretation“ under the term „minimal interpretation“.This is a very good example for why I thik that quantum states are better interpreted in an epistemic sense and why the collapse hypothesis leads to problems with locality and causality.
My view is that the correlations, as all probabilistic relations of quantum systems, are described by the state of the system, and the state of the system is determined by preparation. The preparation in that case is when the entangled photon pair is created (e.g., by parametric downconversion by shooting a laser beam into a crystal).
I would not call this "hidden variable interpretation" but "agnostic interpretation". There are identical members in the ensemble behaving differently when being observed. A hidden variable theory would try to present some reason / mechanism / property / ... that would cause this difference. The minimalistic interpretation doesn't do this: there is no such mechanism, and one simply does not ask for such a mechanism.No answer means: Hiding a „hidden variable interpretation“ under the term „minimal interpretation“.
Which means there can't be "absolute time" or "absolute simultaneity", as you were claiming before. Are you now retracting those claims?There is no problem for them sitting next to each other with at a different age.
I don't think this is correct; measurements on the two entangled electrons should still commute.measuring the youngest batch before the oldest should lead to different result then the doing it the opposite.